The present invention relates to an arrangement for recirculation of exhaust gases of a supercharged combustion engine according to the preamble of claim 1.
The technique known as EGR (Exhaust Gas Recirculation) is a known means of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for supply of air to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's cylinders in which the combustion takes place. Adding exhaust gases to the air causes a lower combustion temperature which results inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used for both Otto engines and diesel engines.
Providing such recirculation of exhaust gases involves arranging a return line in an engine space of the vehicle. The purpose of such a return line is to lead the exhaust gases from an exhaust line arranged on the warm side of the combustion engine to an inlet line for air arranged on the cold side of the combustion engine. The return line comprises a plurality of components such as an EGR valve for controlling the exhaust gas flow through the return line, an EGR cooler for cooling the recirculating exhaust gases, and pipeline portions for leading the exhaust gases from the warm side to the cold side. The location of the EGR cooler in the vehicle is usually such that the return line has to be unnecessarily long and space-consuming.
The amount of air which can be supplied to a supercharged combustion engine depends on the pressure of the air but also on the temperature of the air. In order to supply as large an amount of air as possible to the combustion engine, the compressed air is cooled in a charge air cooler before it is led to the combustion engine. The compressed air is cooled in the charge air cooler by ambient air which is led through the charge air cooler. The compressed air can thus be cooled to a temperature which exceeds the temperature of the surroundings by only a few degrees. The returned exhaust gases are usually cooled in an EGR cooler which uses the coolant of the combustion engine's cooling system as cooling medium. Such an EGR cooler is therefore subject to the limitation that the exhaust gases cannot be cooled to a lower temperature than the temperature of the coolant. The cooled exhaust gases are therefore usually at a higher temperature than the cooled compressed air when they mix in the inlet line to the combustion engine. The mixture of exhaust gases and air which is led to the combustion engine will therefore be at a higher temperature than the compressed air which is led into a corresponding supercharged combustion engine without recirculation of exhaust gases. The performance of a supercharged combustion engine equipped with EGR will thus be somewhat inferior to that of a supercharged combustion engine not equipped with EGR.